Microbiology Rotation Final Exam

The microbiology laboratory receives a genital culture from a 28-year-old female. The specimen direct Gram stain reveals, gram-positive cocci in clusters and gram-negative cocci in chains. The microbiologist inoculates a sheep blood agar plate, a chocolate agar plate, a modified thayer martin plate and a LIM Broth (selective enrichment for group B streptococci). The second shift microbiologist identifies the discrepancy and must take corrective action. The discrepancy indicates:

the preliminary Gram stain was erroneously reported.

Which specimen is quantitatively plated by using a calibrated loop?

Urine

Laboratory specimens for the detection of infectious disease should be collected:

all of the above.

The value of indirect Gram staining from a broth culture in comparison to an agar plate culture is:

organisms tend to demonstrate natural cell shape and arrangement in liquid medium.

The acid-fast stain is specifically designed for bacteria whose cell walls contain:

 

mycolic acids.

Which category of media can be described as containing one or more agents that are inhibitory to all organisms except those being sought?

Selective

Colonies that appear white and shinny are also considered:

opaque.

In which category of media would blood agar best fit?

Differential

Isothermal amplification techniques, such as NASBA, utilize a single temperature for nucleic acid amplification thereby eliminating the need for thermal cycling instruments to precisely and quickly alter the reaction temperature. This often reduces the cost associated with molecular testing and infrastructure requirements. In what settings could this be advantageous?

All of the above

The target in the hybridization assay can be described as:

originating from the unknown organism to be detected or identified.

Which type of hybridization method would be the optimal choice to use to detect a lesion infected with a particular virus?

In situ

The primary advantage for the implementation of a multiplex immunoassay is:

increased productivity and throughput.

The presence of which of the following antibodies usually indicates a recent or an active infection?

IgM

A positive latex agglutination test was observed in a sample containing Cryptococcus spp. The specimen of choice to identify this pathogen is:

cerebrospinal fluid (CSF).

Antimicrobial agents that usually kill target organisms are said to be:

bactericidal.

Extrachromosomal DNA which can serve as virulence or resistance factors and may be transferred from one bacterium to another are -

plasmids

In the microdilution broth dilution method, the interpretive criteria for the susceptible, intermediate, or resistant categories are based on the:

correlation of the MIC with serum-achievable levels of the common doses of the antimicrobial agent and therapeutic outcomes based on clinical studies.

The serum bactericidal test (SBT) involves:

using the patient’s serum to detect its bacteriostatic and bactericidal activity.

Enterococcal resistance to ampicillin predicts resistance to:

cephalosporins.

The minimal bactericidal concentration (MBC) test:

is the antimicrobial concentration that yields a 99.9% reduction in CFU/mL, compared to concentration of the original bacterial inoculum.

The first identification test performed on a clinical isolate of gram-positive, catalase-positive cocci would likely be the:

coagulase test.

Which group of bacteria is described as catalase positive and is gram-positive cocci that grow facultatively anaerobic and form grapelike clusters?

Staphylococcus

Gram positive cocci are isolated from a urine culture with a colony count of greater than 100,000 colony forming units per ml.The organism has the following biochemical characteristics:

catalase = positive coagulase = negative urease = positive

mannitol fermentation = positive arginine dihydrolase = negative novobiocin = resistant (positive)

This organism is most likely?

Staphylococcus saprophyticus

The Staphylococcaceae staphylococcus that is more likely to cause uncomplicated urinary tract infections in nonhospitalized hosts, especially sexually active young women, is:

S. saprophyticus.

Which of the following must be placed in a CO₂ incubator (5-10% CO2) or candle jar because it requires increased CO₂ for best growth (organisms exhibiting this behavior are referred to as being capnophilic)?

S. pneumoniae

Beta hemolytic colonies are seen on the blood agar plate of a throat culture.  The colonies are small and transparent, with large zones of beta hemolysis.  The organisms are catalase negative, gram positive cocci which are:

hippurate hydrolysis = negative PYR hydrolysis = positive Voges-Proskauer = negative

bacitracin = sensitive (positive) arginine dihydrolase = positive ribose fermentation = negative

The identity of these organisms is most likely:

S. pyogenes 

A few large, translucent, beta hemolytic colonies are observed on the blood agar plate of a vaginal specimen sent for culture and susceptibility testing.

Given the following biochemical results, identify this catalase negative, gram positive cocci.

hippurate hydrolysis = positive
PYR hydrolysis = negative
Bacitracin susceptibility = negative
Voges-Proskauer = positive
Arginine dehydrolase = positive

The identification of this organism is -

S. agalactiae

Generally speaking, nutritionally variant streptococci require what ingredient not found in most conventional media?

Vitamin B₆

Large, spore-forming, gram-positive bacilli are recovered from a rice dish suspected of being the cause of an outbreak of food poisoning. Persons affected began to vomit about 5 hours after consumption of the tainted foodstuff. The organism exhibited the following biochemical characteristics

catalase test = positive

H₂S production = negative

motility = positive

hemolysis = large zones of beta hemolysis

hippurate hydrolysis = negative

esculin hydrolysis = negative

This organism is most likely -

Bacillus cereus

A pharyngeal specimen is inoculated on cystine-tellurite blood agar, modified Tinsdale agar, and MacConkey agar. After 48 hours of incubation, black colonies with a brown halo are observed on the Tinsdale agar and gray colonies are isolated from the cystine-tellurite agar. However, no growth is observed on the MacConkey agar. Which one of the following statements explains this discrepancy?

No discrepancy is present; this organism does not grow on MacConkey agar.

The reverse Christie, Atkins, Munch-Petersen (CAMP) test is positive for these curved gram-positive bacilli. Which β-hemolytic organism is used in conjunction with this organism in the reverse CAMP test?

S. aureus

Nocardia spp. form branched filaments that extend into the air that are called _____ hyphae.

aerial

Colony morphology with characteristic ‘swarming’:

Proteus mirabilis

On MacConkey agar, Serratia spp. would appear:

red

An oxidase negative, non-lactose fermenting, gram negative rod is isolated from the stool of a patient with a febrile, gastrointestinal illness. The organism exhibits the following biochemical characteristics:

TSI = K/AG

Hydrogen sulfide production = positive

Citrate utilization = positive

Ornithine and lysine decarboxylase = positive

Arginine dihydrolase = positive

Indole production = negative

This organism is most likely:

Salmonella typhimurium

A gram-negative bacillus that is hydrogen sulfide (H₂S)-positive, citrate-positive, spot indole–negative, and associated with gastroenteritis in the United States is most likely:

Salmonella enteritidis.

The primary drug of choice for infections caused by S. maltophilia is:

trimethoprim-sulfamethoxazole.

In addition to cystic fibrosis patients, patients with which other disease are at greatest risk of death due to fulminant lung infections and/or bacteremia caused by B. cepacia?

Chronic granulomatous disease

Not including organisms in the Enterobacteriaceae family, the most common gram-negative bacilli encountered in clinical specimens are:

Pseudomonas.

Quality control was performed to determine the validity of urea agar. S. multivorum and E. meningoseptica were used, which yielded positive for S. multivorum and negative for E. meningoseptica. Which one of the following statements explains this discrepancy?

No discrepancy is present; the results are valid.

A community hospital microbiology laboratory is processing significant numbers of stool cultures because of an outbreak of diarrhea following heavy rains and flooding in the county.  A media that should be incorporated in the plating protocol is:

Thiosulfate citrate bile salts sucrose for Vibrio species (TCBS)

Vibrio parahaemolyticus often causes gastroenteritis but may be an important cause of ____________ following seashore injuries.

cellulitis

Testing for differentiation of M. nonliquefaciens and M. osloensis can best be performed by:

the ability to utilize acetate.

Quality control performed on indole reagent should be performed on which two organisms?

E. corrodens and W. virosa

Quality control should be performed on which two organisms to determine the validity of the nitrate reduction test?

P. multocida and Suttonella indologenes

Which of the following biochemical reactions identifies an organism associated with blood, bone, and joint infections in young children?

Negative catalase, negative nitrate reduction, and negative indole

Chancroid is the sexually transmitted disease caused by:

Haemophilus ducreyi.

The virulence of this organism, which causes chancroid, is most likely attributed to:

capsular factors.

Although biochemical methods are available for identifying the Bartonella species, limitations exist the limitation for identification is due to which of the following?

The organisms are essentially biochemically inert.

The majority of human infections with Campylobacter species are caused by:

contamination of food, milk, or water with animal feces.

Who is at most risk to develop legionnaires’ disease?

65-year-old transplant recipient

The animal reservoir for Brucella melitensis is:

sheep or goats.

The mode of transmission of B. pertussis can best be described as:

person-to-person contact.

The specimen of choice to collect in suspected cases of Francisella tularensis is:

lymph nodes.

A laboratory assistant that works with mice recently noticed that their lymph nodes were swollen and that they had a lesion on their hand that was not there a few weeks ago. The lymph node tissue is sent to the laboratory for culture. The laboratory technologist noticed on the stained sample that there was an organism present that resembled a spiral, gram negative with flagella. The cultures grew no organisms. What is the most likely cause for the discrepancy?

The organism is not able to grow on media and requires another method for identification.

The differentiation of the similar M. catarrhalis and Neisseria can be best accomplished by:

carbohydrate utilization testing.

Moderate growth of oxidase positive, gram negative cocci are isolated from nasopharyngeal and throat cultures on a 7 y/o girl with otitis media (ear infection).  Biochemical tests produced the following results:

glucose utilization =  negative maltose utilization =  negative lactose utilization =  negative sucrose utilization =  negative

Growth on nutrient agar at 37° C no growth on Thayer-Martin agar nitrate reduction =  positive DNase production = positive

This organism is most likely:

Moraxella catarrhalis

MTM, Martin-Lewis (ML), and New York City (NYC) media were all developed for the selective isolation of which organism?

N. gonorrhoeae

An anaerobic media, which contains ferric ammonium citrate and hemin, bile salts, and gentamicin, is used to isolate which group of organisms?

Bacteroides spp.

Most pathogenic anaerobic species isolated from clinical specimens are classified as‑

moderately obligate anaerobes

Incubation conditions for anaerobic cultures include:

incubation for 48 hours before exposing the culture to air.

The most likely identification of kanamycin-sensitive and anaerobic gram-negative bacilli that fluoresce a chartreuse color is:

Fusobacterium spp.

A scotochromogen is isolated from a sputum specimen from a leukemia patient after a growth period of 21 days. Additional biochemical characteristics include:

niacin production: negative

nitrate reductase: positive

tween 80 hydrolysis: positive

arylsulfatase: positive

urease production: positive

This organism is most likely -

M. szulgai

Quality control is performed to test the validity of catalase production at 68°C. M. fortuitum and M. tuberculosis are used, which yield a positive and negative reaction, respectively. Which one of the following statements explains this discrepancy?

No discrepancy is present. M. fortuitum is catalase-positive and M. tuberculosis is catalase-negative at 68°C.

The Runyon system of classification is based on:

growth rate and colonial pigmentation.

Etiological agent of Q fever?

Coxiella burnetii

Which group of drugs is effective against M. pneumoniae infections?

Fluoroquinolones

The etiologic (causative) agent of pinta is:

Treponema carateum    

Leptospira interrogans ss. icterohaemorrhagiae is the etiological agent of –

Weil's disease

The native hosts of Leptospira interrogans ss. canicola are-

Dogs  

A 59-year-old patient with cancer who was receiving high doses of chemotherapy developed a secondary lung infection that was identified as a fungus. The organism disseminated, which ultimately was fatal to the patient. The organism isolated from sputum exhibited septate hyphae that were dichotomous. The organism is most likely which of the following?

Aspergillus

An example of a thermally monomorphic mold is:

Epidermophyton.

A pulmonary fungus ball and external otomycosis and onychomycosis are all infections caused by which genera?

Aspergillus

Which organism produces mostly shades of green or blue-green colonies? Microscopically, hyphae are hyaline and septate and produce brushlike conidiophores.

Penicillium

Macroscopic examination of granules from lesions of mycetoma reveals them to be white to yellow and 0.2 to 2 mm in diameter. Microscopically, the granules consist of loosely arranged, intertwined septate hyaline hyphae cemented together. Which organism can cause a mycetoma infection?

P. boydii

The cell membrane of P. jirovecii contains _______ rather than _______, which differentiates it from other fungi.

cholesterol; ergosterol

A patient with acquired immunodeficiency syndrome (AIDS) notices skin lesions on his back that have begun to ulcerate. Upon physical examination, his physician also notices hepatomegaly that is most likely caused by hepatitis. The physician prescribes antifungal therapy to prevent the dissemination of which of the following yeasts?

C. neoformans

The chief source for the distribution and maintenance of _________________ is pigeon excreta.

Cryptococcus neoformans

A patient is diagnosed with an invasive Aspergillosis infection. The antifungal therapy that should be administered is:

amphotericin B.

Leptospira interrogans ss. icterohaemorrhagiae is the etiological agent of -

Weil's disease

If tachyzoites are found circulating in blood, then the infection would be classified as a:

parasitemia.

A bronchoscopy sample with the request for culture of Legionella is sent to the laboratory.  The correct plating protocol is:

Culture on buffered charcoal yeast extract agar with antibiotics (BCYE)

Bacterial pneumonia in children is most commonly caused by:

Staphylococcus aureus.

Adenoviruses are one of the most common etiologic agents of lower respiratory tract infection among:

previously healthy patients 2 months to 5 years of age.

Which of the following is a life-threatening, non-suppurative (no pus production) and non-invasive condition associated with S. pyogenes infection which can lead to kidney failure?

acute glomerulonephritis  

Most cases of pharyngitis occur during the colder months and are primarily caused by:

viruses.

The innermost membrane layer surrounding the brain and spinal column is the:

pia mater.

Which of the following is an important cause of neonatal sepsis (as a result of colonization of the vaginal tract of pregnant women)?

S. agalactiae (group B)

The organism that can be encountered in the conjunctival sac and that exists as indigenous microbiota is

Staphylococcus epidermidis.

Complicated and uncomplicated urinary tract infections can be differentiated according to which of the following?

An uncomplicated urinary tract infection does not reoccur and is not associated with other structural or physiological abnormalities.

Biologic false positives may occur in serologic assays for syphilis as a result of:

Pathologic conditions, including other infectious diseases

The type of vaginitis referred to as bacterial vaginosis is thought to be caused by:

Gardnerella vaginalis.

The predominant organism in vaginal secretions from normal women of reproductive age is:

lactobacilli.

Stool received for routine culture in most clinical laboratories in the United States should be examined for the presence of at least:

Campylobacter, Salmonella, and Shigella spp.

________________ may cause a gastrointestinal illness indistinguishable from appendicitis.

Yersinia enterocolitica

A patient is diagnosed with gas gangrene in the skin as a result of bullous lesions associated with sepsis. The Gram-stain reaction and morphologic features of the most probable pathogen causing this infection is:

gram-positive bacilli.

This organism colonizes the oral cavity of a variety of animals, especially cats and dogs and therefore is commonly isolated from cat and dog bites.  What is the name of this organism?

Pasteurella multocida

Bone marrow is not generally used for the identification of systemic infections including bone infection because:

blood cultures are equally as useful for any bacteria that may be present in the marrow.

A 76-year-old man attends a meeting at his condominium association where many of his neighbors are sick with respiratory symptoms. He later develops a Haemophilus influenzae infection, which is classified as a _________ infection.

community-acquired

Bioterrorism is a term used to describe the act of using

microorganisms to harm the civilian population intentionally.